Stove for blast furnace operation



Feb. 25, 1964 J. E. M DONALD 3,122,359

STOVE FOR BLAST FURNACE OPERATION Filed Dec. 8, 1961 2 Sheets-Sheet 1 BLAST FURNACE 5 +76 75 COLD TO STACK BLA ST 26 INVENTOR. I00 Jqzwss .5. Mac 001 g wfw J. E. M DONALD STOVE FOR BLAST FURNACE OPERATION Feb. 25, 1964 2 Sheets-Sheet 2 Filed Dec. 8-, 1961 r. C A N E U F T S A L 5 2. E N R U B 5 A G NATURAL GAS OR 01!. BURNER NATURAL GAS O2 OIL BURNER BLAST FURNACE GA 5 BURNER o D s 5 L Y H ON 5 G N J If M 5 T S Ml M FLUE.

3,122,359 T=3VE F93 BLAST FURNAQYE OPERATEON James E. MacDonald, 713 Highland Ave., Latrobe, Pa. Filed Dec. 8, i961, Ser. No. 157,989 2 Claims. (Cl. 263-3) This invention relates to a stove for blast furnace operation and the like wherein air or other combustion supporting gas is preheated, then transmitted in heated condition to the blast furnace for blast furnace operation. It has been found that by increasing the heat content of the combustion-supporting gas it is possible to effect substantial savings in coke consumption in blast furnace operation. It has been estimated, that by increasing the temperature of the gas, as provided by my invention, it is possible to effect as high as 13% saving of coke consumption, this amounting to a substantial dollar saving in blast furnace operation.

in previously employed stoves for preheating air, the maximum temperature to which the air can be heated is limited by the ability of certain members of the stove to withstand high temperature. Should the temperature of the stove be in excess of the heat resistivity of certain of the stove members, and particularly the metal members, then it is possible to do such damage that the oven will be rendered inoperative and therefore to stay within the capacity of the oven, 1 found that the upper limit of temperature to which the air can be heated is inherently limited in prior art structures.

It is therefore an object of the present invention to provide a heating process and a stove structure, for developing higher heating temperatures of the air or other combustion-supporting gas while remaining within the heat capacity of the stove and to accomplish these ends without adding substantial cost or additional components to the stove.

Moreover, it is an object of the invention to effect a revision of existing stove structures to increase their capactiy for containing heat and as a consequence thereof I can obtain an increased temperature of the preheated air with its attendant advantages in blast furnace operation.

it is a further object of the invention to provide a dome constructed combustion chamber which utilizes more efficiently the interior volume of the stove by disposing therein a greater volume of heat-absorptive refractory material so that the total potential heat content within me interior of the stove is thereby increased. Consequently, I obtain a more efficient operation for a given volumetric capacity of stove by utilizing more completely the volumetric capacity of the stove.

A further object of the invention is to provide a heating stove construction which can utilize a low calorie content fuel such as blast furnace gas, having typically about 80 Elm. per cubic foot and to utilize such low heat content gas without detracting from the higher operating temperatures which are generated and are required for obtaining greater preheat of the air. Related to this object, is a further object of providing a heat-generating process and equipment whereby low E. content gas such as blast furnace gas can either be enriched, or preheated, or both in order to utilize most efiiciently such low calorie content fuel in generating heat which is intended for storage wit in the refractory mass of the stove during the heating cycle.

A still further obiect of the invention is to provide preheated combustion-supporting gas such as air and which can be transmitted in its heated condition to the blast furnace without losing a significant portion of the heat thereof during delivery from the stove to the blast furnace.

Fatented Feb, 25, 1964- Egg A further object of my invention is to provide a blast furnace stove constituting an improvement over the blast furnace stov structure shown in my copending application SN. 86,395, filed February 1, 1961, now abandoned, and which is incorporated in the present application by specific reference.

()ther objects and features of the invention will become apparent from a consideration of the following description, which proceeds with reference to the accompanying drawings, wherein:

FIGURE 1 is a sectional elevation view of the stove, together with preheating recuperators which can be used in some phases of operation to preheat the incoming air and low B.t.u. content fuel which is used for combustion;

FIGS. 2 and 3 are sectional views taken respectively on section lines 2-2 and 33 of PEG. 1;

FIG. 4 is an enlarged sectional view taken on line 44 f FIG. 3; and

FIG. 5 is an enlarged sectional detail view taken on line 5-5 of FIG. 3.

Referring now to FIG. 1, the stove designated generally by reference numeral if; is a vertical, generally cylindrical construction ty ally of about feet in height and 21 feet in diameter with three of four such stoves for each blast furnace. The stove includes an outer steel shell 12 and a lining 14 of wall brick which can vary, but is typically about 3 /2 inches thick and is of a heat resistant fired brick composition. These parti ular construction details do not form an essential part of the present invention.

At the bottom of the stove and resting on a suitable reinforced base 16 are a plurality of support columns which are metallic blooms or the like and which, while having sufificient strength to support the overhead load of refractory checkers 2b are incapable of sustaining excessive temperatures without weakening and in the event of failure will cause collapse of the overhead structure. It should be understood that there is a substantial overhead load of refractory material, the order of 600-806 tons of refractory checkers and therefore the metal col umns must be sufficiently protected against destructive heats since the cost of reconstruction of the stove in the event of failure of the support member would be quite high.

To protect these 0 urnns against overheating, 1 provide a cooling condui 22 having coils which are wound around each column and are connected in series to protect each column, the inlet 24- for the conduits being controlled by a valve 25 which may be thermostatically operated to provide for shutting off and turning on the flow of water Within the conduit 22. The cooling coil terminates in an outlet 23 and a return line 3% leads to a heat exchanger 32 winch effects cooling of the water efore it reaches a return line 34 for recycling and abstracting heat within chamber 36 containing the support columns 18. In this fashion, the heat which is contained within chamber 38 and is a sorbed by the checkers 2i? therein is prevented from overheating the columns.

Each column has a support head in supportive engagement with an associated cross-seam 42 there being sufficient, equally spaced transverse support beams to carry the load of the checkers and transfer such load to the columns. The support beams, also being metal, ar surrounded by protective cooling coils which protect the steel members against overheating and consequent failure because of exposure to the high tern; ra tures within chamber 33. The cooling coils can be interconnected with the coils which are turned about the columns 18 or these coils can be separately connected and cooled, depending upon design pref rence. Vl nere the lines 22 enter and leave the chamber 56 the ceramic wall is insulated with Fiberfrax to prevent heat loss and also to prevent gaseous leakage from the chamber 36.

The beams or girders have a number of steel grid bars 5%} which extend transversely of the girders 42 and each of which includes a conduit section 52 for receiving a protective flow of water coolant or the like. The steel grid bars 50 are bridged by cast iron checker supports 54- and the resulting pattern of grid bars 50 and cast iron checker supports 5% to provide support for the bottom course of refractory checker members 48 which can be of any suitable construction in composition, best adapted to absorb heat and therefore constitute a heat reservoir which, after being heated, will release said heat to incoming air.

Suitable checker constructions are disclosed in US. Patents 2,034,820 and 2,438,814, both of these patents being herewith incorporated by reference. The checkers can be constructed of firebrick which is especially designed for efficient heat transfer and is of dense compact construction having a kdgh thermal conductivity and a sufficient refractoriness to withstand temperatures which are encountered within the stove.

The checkers are spaced to provide vertical dues or passages providing for passage of gaseous fiow vertically Within the chamber 38 which is substantially filled with checkers 20 which serve both as the heat absorbing and the heat releasing medium. The particular pattern of distribution of the checkers does not form a part of the present invention and it is possible to provide columnar or any other suitable packing arrangement of the checkers in either weave or non-weave type arrangement.

At the uppermost part of the stove is a dome combustion chamber 53 which is surmounted by a refractory lining as. The combustion chamber 58 receives a flow of gases including a low calorie content blast furnace gas from line 62, this gas containing typically about 80 B.t.u. per cubic foot and is combined with a flow of air from line 64. The two lines as, are separated so that there is no mixing of the two gases which are apt to be explosive when mixed together if they are in heated condition. In order to utilize all of the caloric content of the low B.t.u. gas, it is desirable in some applications to preheat both the air and the gas by means of recuperators 66 and 58, there being a suitable valve 70 and bypass line 72 for each recuperator in order that all or any preferred portion of the low B.t.u. content gas and air can be heated before enter ng the combustion chamber 58. I have also found it advisable, in order to effect complete burning of the blast furnace gas, to have the chamber 5% preheated to a level of about 2000 P. so that when the blast furnace gas enters the chamber it is more readily combustible.

For preheating the chamber 58, and also for enriching the caloric content of the gas for some applications of operation, I provide an inlet line 74- for introducing a higher caloric content fuel such as natural gas, manufacturers gas or atomized oil. These gases are properly mixed with air and pressurized to form a jet burner within chamber 553. This arrangement is especially suited for a variety of firing arrangements for the stove, in which I can use blast furnace gas which is readily available, and is economical to use since it is produced as a by-product of blast furnace operation. To the extent that I can maximize the use of this readily available but low caloric content fuel I can effect greater economies of operation.

At the initial part of the heating cycle of the stove I raise the temperature of the heating chamber 53 by means of burning high caloric content fuel which sufficiently raises the temperature of the chamber 58 to increase the combustibility of the blast furnace gas. Should the blast furnace gas ever become in short supply it is possible to run entirely on the higher caloric content fuel or alternatively to use any pronortionof blast furnace gas plus higher heat content fuel. The described arrangement provides a substantial advantage in stove operation because of the greater selection of fuel combinations and fuels including the economical blast furnace gas fuel.

When a substantial volume of gas is used having a low caloric content the gaseous ilow tends to absorb an inordinate amount of the heat of combustion thereby preventing attainment of operating temperatures as high as I contemplate them in stove operation and therefore, to prevent supttering and incomplete combustion, l elimi nate these difiiculties of incomplete combustion and waste and heat loss by confining oxidation Within a dome chamber having a substantially smaller surface area to volume ratio and immediately followiru oxidation passing the gaseous flow directly downwardly through the flue passages. By means of the dome construction, I confine the heat more adequately than was previously the practice with a vertical chamber extending the height of the stove and I then abstract larger qunatities of heat from the mass of gas which is itself elevated in temperature during combustion, by passing it immediately through the flue passages where the heat is transferred to the refractory checkers 20.

Since substantially the entire cross-section of the stove is filled with refractory checkers and for substantially the entire height of the stove the heat absorptive medium is greatly increased over prior art structure, it being appreciated that in order to abstract the maximum amount of heat from a low caloric content gas it is essential to provide the maximum heat exchange surface area because of the substantial flow of gas.

After the combustion process takes place in chamber 53 and the gases have flowed vertically downwardly through the flue passages they pass (wavy line arrows FIG. 1) through a stack opening 76 having a stack valve '78 which is open during the heating stage of operation of the stove. The valve 73 is thereafter closed when sufficient heat content has been absorbed by refractory checkers. The heat which is generated within the heating chamber produces a combustion chamber temperature of about 2700 F. and there is a substantial temperature gradient through the mass of refractory checkers, this gradient reaching a temperature of about 8001000 F. at the bottom course of refractory checkers.

In previous constructions, the heating cycle was terminated before the heat at the bottom of the stove became sufhciently high enough to deteriorate the metal support members comprising the columns 18, grid bars 50 and cast iron checker supports 5 As a consequence thereof, the heating had to be terminated before the refractory mass reached its maximum heat absorptive capabilities and therefore limited the extent to which air could be heated by passing upwardly through the heated refractory mass of checkers. In order therefore to obtain a higher temperature to the air when it is up-blasted through the refractory mass, it was necessary to increase the heat content of the refractory checkers which is possible only by shielding the heat sensitive metal members against the higher temperatures generated within the refractories, this being accomplished by the cooling coils 22-, 44 and 52. Instead of the previous upper limit of 500-700 F. temperature for the exit gases, I am now able to utilize exit temperatures in the range of 800-1000" F. and thereby substantially increase the heat content of the refractory mass because more absorptive media is provided and said media is heated to a higher temperature.

Following the heating cycle, the valve 80 for the inlet combustion gases is closed, valve 32 for the high caloric content fuel in line '74- is closed and valve 78 leading 'to the stack is closed and a cold air blast line is opened causing a continual draft of air under pressure to pass into chamber 36 and then pass upwardly through the flue passages defined by the refractory checkers and which are graduated in cross-section to accommodate for the expanding volume of the air as it becomes heated. Thus, the cross-sectional area of the flue passages at the lowermost part of the stove is the smallest area and is gradually increased to become the maximum area at the uppermost part of the stove. The air then enters combustion chamber 58 in its heated condition, the temperature being about 1800-1900 F. and then enters line 85 through the now-open valve 83. The line is formed in sections 84, 86 and 83 which are supported by brackets 90 exteriorly of the stove, said line 85 terainating in a hot blast line $2 which conducts the heated gas to the blast furnace for blast furnace operation. "I he joints 94 conmeeting the sections are formed of Fiberfrax which is a heat-resistant non-conductive refractory which makes an excellent insulating material, does not deteriorate under high temperatures and is sufficiently resilient to provide for limited differential expansion between the sections. In order to make the weight of the conduit 80 as small as possible to facilitate supporting thereof from the side of the oven, 1 provide a ceramic castable lining 95 having a smooth surface to permit the necessary velocity internally of the conduit. The lining has suitable insulating properties so that air which is elevated in temperature to about 1900 F. can be transmitted to the blast furnace without appreciable heat loss of the air which is at an average temperature of about 1700 F. at the time it reaches the blast furnace. It is estimated that by using air which is preheated from the previously used 1500 upper limit to the present value of 1700 F. at the blast furnace bristle pipe, I will effect a saving of about 280 pounds of coke per ton of iron produced by the blast furnace. This saving is a substantial dollar saving per year of blast furnace operation.

Stove Operation The operation of the stove is believed obvious from the foregoing description, however, the following explanation of a complete cycle of heating and then air blasting will be provided to summarize the invention.

At the initial stage of use, the mass of refractory checkers designated by reference numeral 39 is first heated up to provide a heat reservoir which then releases its heat to the air when air is up-blasted through vertical flue passages which are defined by the refractory checkers.

To heat up the refractory checkers there is burned with n chamber 53 a combustible fuel which can utilize a variety of caloric content materials, including blast furnace gas which is produced as a by-product of blast furnace operation and has characteristically a low caloric content, typically of about 86 Btu. per cubic foot. Since the blast furnace gas is readily available in abundant quantity as a by-product of blast furnace operation, it is advantageous to use this gas to the maximum extent. When blast furnace gas is used, the chamber 58 is pre heated by injecting a high caloric content fuel such as natural gas or the like through line 74, thereby heating up chamber 58 making the blast furnace gas more readily combustible, the blast furnace gas being brought in through line as and then mixed at its outlet and within charnber with the proper proportions of air from line s4. The last furnace gas may be made even more readily combustible by passing both it and the inflow of air through recuperators ss, 68 to raise the temperature of the blast furnace gas to about 800 F. or so. When the gases are burned within chamber 58, heat is liberated which is absorbed by the mass of refractory checkers and the combustion gases are passaged downwardly through the vertical fines and effect heat exchange with the refractory ChECrifIS as they passage therethrough and then exit through the stack line 7e, valve 73 being opened during this stage of operation and valve 1% of the cold blast air line 98 being closed as well as valve 83 of the heated air outlet leading to line 35.

The combustion chamber will reach temperatures of about 27-30" F. and the heating cycle, will continue until the bottom course of checkers reaches a temperature of about 800-1860" F. A previous limitation on stoves of the prior art was that heating of the refractory checkers had to be terminated within the heat-resistant limitations of the metallic columns 13 and girders 42 which support the heavy overhead load because being exposed to the heat of the refractory mass, they could become deteriorated sulficiently to cause collapse of the refractory mass within chamber 33. This factor is no longer a limitation on the heating stage of the stove since I provide at the start of the heating cycle for the passage of cooling liquid through conduits 22, 44 and 52 which protect the metallic supporting structure against the effects of heat and therefore it is possible to carry on heating to a greater extent, storing greater quantities of heat within the refractory checkers 21' The refractory checkers 21 are heated non-uniformly throughout the height of the stove, reaching their highest temperature at the uppermost portion and the coolest temperature at the lowermost portion. Since the exit temperature of the combustion product gas is increased from the previous upper limit temperature range of 500-700" F. to a new upper limit of 8604000 F. there is a consequent increase of total heat within the refractory mass which is available for increasing the temperature of air which is heated in the manner next to be described and the heating of the air can continue for longer periods of time.

When the heating operation is completed the valves '78, 8d, 82 are closed to prevent further inlet of combustible gas and outlet thereof through the stack valve 78. Valve fill in the cold air line 9% is then opened and the cold air travels upwardly under forced draft through the vertical flue passages defined by the refractory checkers. The air ecom'es successively hotter as it travels upwardly through the stove and attains an upper limit of about l800l-9 F. after passing through the refractory checkers as compared to the previous upper limit of 16001700 F. The heated air then passes through the open valve 83 and passages downwardly through the line $5 and enters the hot blast line 92 where it is transmitted to the blast furnace for blast furnace operation. The higher temperature of the preheated air, i.e., the increase of 200 F. in heat content enables a saving of coke consumption per ton of iron produced by blast furnace operation.

One of te advantages of the present invention is that a greater variety of fuel can be used, including the eco nomical and readily available blast furnace gas. Should however the supply of blast furnace gas become for any reason short in supp y, I can operate entirely on higher caloric content such as natural gas, water gas or other fuel of a similar nature. Or, I can utilize a combination of blast furnace gas and high caloric content gas or, use only the blast furnace gas, improving its combustibility by preheating or not with a suitable recuperator arrangerncnt.

After heating is completed of the refractory checkers the following air heating cycle will last approximately three hours or so, this being an increase in blast time over the previous stoves which were available because there is an increase of refractory heat absorption medium and the medium is itself heated to a greater extent.

Although the temperatures to which I preheat the air for last furnace operation are higher, I am still able, by the use of the present invention, to use low calorie content fuels, this being a surprising result previously thought unattainable by those skilled this art because of the belief that low caloric content fuels had reached an upper limit in their ability to generate greater heating of a refractory mass and then a transfer of the heat content of the mass to air for blast furnace operation. Contrary, however, to the self-imposed limitations of the art, I have found that it is possible to increase the temperature of air which can be heated by a refractory mass by using a low calorie content fuel, and without producing damage to the heat-susceptible metallic members of the stove. This result is accomplished by a novel arrangement of a heating chamber which is disposed at the uppermost part of the stove to obtain a greater quantity of heat-absorptive refractory medium, and by further provision of means for confining the heat to the refractory mass which shields the heat sensitive part of the stove. it is therefore possible to achieve higher heat content of the refractory mass which acts as an accumulator of the heat and then releases said heat to the air.

Although the present invention has been described in connection with a single example embodiment, it will be readily understood by those skilled in the art that this is illustrative of the invention and is in no sense restrictive thereof, It is reasonably to be presumed that those skilled in this art can make numerous revisions and adaptations of the invention to suit individual design requirements and it is intended that such revisions and variations which incorporate the herein disclosed principles will be included within the scope of the following claims as equivalents of the invention.

I claim as my invention:

1. A process for heatin" a current of air or other combustion-supporting gas for usage in blast furnace operations or the like, comprising the steps of injecting a flow of low caloric content combustible gas and air through the bottom portions of the side of an elevated dome chamber of a refractory-lined stove having a cross section thereof substantially filled with heat-absorbing bodies defining vertical fiues therein, effecting burning of said loW caloric content gas as it travels in a generally horizontal path without direct impingement on said heat-absorbing bodies and causing the burned gas to thereafter flow downwardly through said fines to store the heat generated by said gas within the mass of refractory material stored within the interior of said stove, channeling an inflow of air which is passed through the line passages of said refractory material and counter-currently to the passage of heat therein to provide heating of the air, and thereafter passing the heated flow of air through heat resistant and heat insulated channel means disposed exterioriy of said stove to eifect distribution of the heated air to the blast furnace.

2. A process for heating a current of air or other combustion-supporting gas for usage in blast furnace operations or the like, comprising the steps of injecting a how of low calorie content combustible gas and air through the bottom portion of the side of an elevated dome chamber of a refractory-lined stove having a cross section thereof substantially filled with refractory heat-absorbing bodies defining vertical flues therein, effecting burning of said low calorie content gas as it travels in a generally horizontal path Without direct impingement on said heatabsorbing bodies and causing the burned gas to thereafter flow downwardly through said lines to store the heat generated by said gas within the mass of refractory material stored within the interior of said stove, injecting an auxiliary high caloric content gas through the bottom portion of the side of said dome chamber and mixing it in predetermined proportion with said first-mentioned combustible gas to effect heat generation raising the tempera ture of the refractory mass to a predetermined level, thereafter channeling an inflow of air which is passed through the flue passages of said refractory material and counter-currently to the passage of heat therein to provide heating of the air, and passing the heated flow of air through heat resistant and heat insulated channel means disposed exteriorly of said stove to effect distribution of the heated air to the blast furnace.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR HEATING A CURRENT OF AIR OR OTHER COMBUSTION-SUPPORTING GAS FOR USAGE IN BLAST FURNACE OPERATIONS OR THE LIKE, COMPRISING THE STEPS OF INJECTING A FLOW OF LOW CALORIC CONTENT COMBUSTIBLE GAS AND AIR THROUGH THE BOTTOM PORTIONS OF THE SIDE OF AN ELEVATED DOME CHAMBER OF A REFRACTORY-LINED STOVE HAVING A CROSS SECTION THEREOF SUBSTANTIALLY FILLED WITH HEAT-ABSORBING BODIES DEFINING VERTICAL FLUES THEREIN, EFFECTING BURNING OF SAID LOW CALORIC CONTENT GAS AS IT TRAVELS IN A GENERALLY HORIZONTAL PATH WITHOUT DIRECT IMPINGEMENT ON SAID HEAT-ABSORBING BODIES AND CAUSING THE BURNED GAS TO THEREAFTER FLOW DOWNWARDLY THROUGH SAID FLUES TO STORE THE HEAT GENERATED BY SAID GAS WITHIN THE MASS OF REFRACTORY MATERIAL STORED WITHIN THE INTERIOR OF SAID STOVE, CHANNELING AN INFLOW OF AIR WHICH IS PASSED THROUGH THE FLUE PASSAGES OF SAID REFRACTORY MATERIAL AND COUNTER-CURRENTLY TO THE PASSAGE OF HEAT THEREIN TO PROVIDE HEATING OF THE AIR, AND THEREAFTER PASSING THE HEATED FLOW OF AIR THROUGH HEAT RESISTANT AND 